This application claims the priorities of Japanese Patent Application No. 2002-180177 filed on Jun. 20, 2002 and Japanese Patent Application No. 2003-152704 filed on May 29, 2003, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a projection type display apparatus for projecting an image displayed on a reflection type light valve using a liquid crystal or the like onto a screen under magnification; and, more specifically, to a projection type display apparatus having a configuration suitable for widening a projection lens.
2. Description of the Prior Art
Recently, the market for projectors has been greatly expanding as personal computers have come into wider use. Known as a light valve for converting images into signals and carrying out optical modulation are transmission and reflection type liquid crystal display devices and DMD devices in which minute mirrors are regularly arranged. Among them, the reflection type liquid crystal display devices are suitable for making highly efficient, minute pixels, and have become a focus of attention as a light valve providing high-quality images. A characteristic feature of the reflection type liquid crystal display device lies in that they distinguish ON and OFF states of a pixel from each other according to polarization directions by utilizing an optical rotation of the liquid crystal.
Known as an example of a projection type display apparatus using a reflection type liquid crystal light valve is one using four polarization beam splitters. Its schematic configuration will be explained with reference to FIG. 13. This drawing shows a state where, in a projection type display apparatus, white light from a light source is decomposed into three color luminous fluxes of R, G, and B, which are then caused to carry image information items by respective reflection type liquid crystal panels corresponding to the individual color light components, and thereafter combined together, so as to enter a projection lens. The paths of individual color light components are schematically illustrated, whereas solid and dotted lines indicate two kinds of polarization states with polarization directions different from each other. In the following explanation, the solid and dotted lines will refer to S-polarized light and P-polarized light, respectively.
Of the white light emitted from a light source which is not depicted, only S-polarized light is transmitted through a polarizing plate 241, or its polarization direction is adjusted by the polarizing plate 241 after being converted into S-polarized light in an upstream stage which is not depicted. The resulting light component is made incident on a polarizing beam splitter prism (hereinafter referred to as PBS) 243 by way of a specific wavelength polarization converter 242. The specific wavelength polarization converter 242 is a device for converting polarization of light in a specific wavelength band, e.g., converting the polarization of G light into P polarization.
Of the luminous flux incident on the PBS 243, the G light, which is in P polarization, is transmitted through the PBS 243, and further a PBS 219, so as to irradiate a reflection type liquid crystal panel (hereinafter referred to as LCD) 221 G for G light. On the other hand, B light and R light, which are in S polarization, are reflected within the PBS 243, so as to be made incident on a PBS 226. A specific wavelength polarization converter 225 is disposed upstream the PBS 226, so as to convert the polarization of B light into P polarization, for example. As a consequence, the B light is transmitted through the PBS 226, so as to irradiate an LCD 221 B for B light, whereas the R light is reflected by the PBS 226, so as to irradiate an LCD 221 R for R light.
The luminous fluxes carrying respective image information items corresponding to the individual color light components are turned into polarized light components different from those emitted from the PBS 219, 226. Therefore, the G light is reflected within the PBS 219, the B light is reflected within the PBS 226, and the R light is transmitted through the PBS 226, so as to be made incident on a PBS 247.
For improving the contrast of projected images, quarter wave plates 220a, 220b, 220c are disposed upstream the LCDs 221G, 221B, 221R. Polarizing plates 218, 222 are disposed on the light entrance side (PBS 243 side) and light exit side (PBS 247 side) of the PBS 219, so as to adjust deviations in polarization directions. A specific wavelength polarization converter 227 is disposed between the PBSs 226 and 247, so as to convert the polarization of B light into P polarization.
The G light, which is in S polarization, is reflected within the PBS 247, whereas the B light and R light, which are in P polarization, are transmitted therethrough, whereby three color light components are emitted as a composite luminous flux. This luminous flux is transmitted through a specific wavelength polarization converter 245, where the polarization of G light is converted into P polarization, and then a polarizing plate 246, where deviations in polarization directions caused by the PBSs are adjusted, so as to be projected by a projection lens 230.
In such a configuration, four PBSs are employed so as to utilize differences in polarization directions of individual color light components in decomposing and combining colors. Therefore, as compared with the case using dichroic devices, polarization characteristics can be maintained more favorably, and the light utilization efficiency can theoretically be made higher. In practice, however, polarization characteristics are hard to maintain when light is transmitted through large polarizing beam splitters, so that the polarization characteristics are likely to be disturbed, whereby the light utilization efficiency cannot always be made higher. Also, the projection type display apparatus may lower its contrast because of disorders in polarization characteristics.
For eliminating such disorders in polarization characteristics, it has been proposed to use a PBS made of a material having a smaller photoelastic constant. However, materials having a very small photoelastic constant may be not only heavy and expensive, but also environmentally problematic since they contain a large amount of lead and the like. Japanese Unexamined Patent Publication No. 2001-154152 discloses a configuration in which the number of PBSs for use is reduced to 2 or 3, in order to overcome these problems.
Meanwhile, projection lenses for recent projection type display apparatus have been prone to widen lenses by shortening their focal length, so that a large image can be constructed even when the distance from the projection lenses to a screen is short. In particular, the demand for widening is strong in projection lenses employed in front type projectors for use in limited spaces such as those for home use, and rear projection TVs which are required to be made smaller and thinner.
However, it is quite difficult to design wide lenses in projection type display apparatus having the above-mentioned configuration. These apparatus are configured so as to dispose at least a PBS on the LCD side and a PBS, a dichroic mirror, or the like on the projection lens side between the LCD and the lens located closest to the light source in the projection lens. When widening the projection lens while maintaining an absolute distance from such a liquid crystal panel to the projection lens, not only the projection lens but also the whole apparatus is likely to become large. This may not be overcome by the lens design alone under circumstances where the whole apparatus is required to be made smaller.
The technique disclosed in the above-mentioned publication disposes a field lens in the vicinity of a light valve, and describes operations and effects obtained when the field lens is considered to be integrated with the projection lens. Though this technique is effective in reducing the size of PBS or dichroic prism, its operations are obtained by breaking a telecentric luminous flux state, whereby it is not always advantageous when illuminance and chromaticity distributions in images are taken into consideration. It is desirable for luminous fluxes to be in a telecentric state when transmitted through a PBS. If a field lens is disposed near a light valve as such, polarization characteristics may be disturbed when light is transmitted through the field lens, which is unfavorable in terms of light utilization efficiency and contrast.
In view of such circumstances, it is an object of the present invention to provide a projection type display apparatus which can enhance light utilization efficiency and contrast while facilitating the widening of a projection lens in conformity to recent technical trends.
The present invention provides a projection type display apparatus chromatically decomposing white light emitted from a light source into color light components, chromatically combining the color light components after image modulation, and projecting a desirable image onto a screen by using a projection lens; the apparatus comprising:
color light decomposing means for decomposing the white light into a first color light component in three color light components and the remaining second and third color light components, and emitting thus obtained color light components into respective directions different from each other;
a first optical device for guiding the first color light component emitted from the color light decomposing means to a first reflection type light valve for optically modulating the first color light component and emitting the first color light component optically modulated by the first reflection type light valve;
a second optical device consisting of a polarization separating/combining device for separating the second and third color light components emitted from the color light decomposing means into the second and third color light components, guiding these color light components to second and third light valves for optically modulating the respective color light components, combining the second and third color light components optically modulated by the light valves, and emitting thus combined color light components; and
color light combining means for combining the first color light component emitted from the first optical device and the second and third color light components emitted from the second optical device;
wherein a first lens comprising at least one lens element is disposed between the first optical device and the color light combining means; and
wherein a second lens comprising at least one lens element is disposed between the second optical device and the color light combining means.
The first optical device may comprise polarization separating/combining device.
Preferably, each of the first and second lenses has a positive refracting power as a whole, the first lens and a third lens disposed on the light exit side of the color light combining means constitute the projection lens, and the second and third lenses constitute the projection lens.
Preferably, polarization direction converting means for converting the white light emitted from the light source into linearly polarized light vibrating in one direction is disposed upstream the color light decomposing means.
Preferably, a polarization converter for converting polarization of light in a specific wavelength band into a polarization direction having a predetermined angle is disposed on a side of the second optical device where a luminous flux from the color light decomposing means is incident. More preferably, a polarization converter for converting polarization of light in a specific wavelength band into a polarization direction having a predetermined angle is disposed on each of sides of the second optical device where a luminous flux from the color light decomposing means is incident and where a luminous flux is emitted to the color light combining means.
The color light combining means may be constituted by a dichroic prism.
The color light decomposing means may comprise color separating means for decomposing incident light according to a wavelength band thereof. The color light decomposing means may be constituted by a polarization converter for converting polarization of light in a specific wavelength band into a polarization direction having a predetermined angle, and a polarization separating device for separating incident light according to a polarization direction thereof.
Preferably, a polarizing plate is disposed on the exit side of each of the first and second optical devices for light directed to the color light combining means. Preferably, a polarizing plate is disposed on the entrance side of each of the first and second optical devices for light from the color light decomposing means.
The reflection type light valves may comprise reflection type liquid crystal display devices.
In another aspect, the present invention provides a projection type display apparatus comprising:
three-color light combining means for combining a first color light component of three primary color light components with the remaining second and third color light components, the first and the remaining second and third color light components being incident on the three-color light combining means in two directions different from each other after being optically modulated by respective reflection type light valves corresponding to the three primary color light components;
two-color light combining means for combining the second and third color light components;
a first lens disposed between the three-color light combining means and the reflection type light valve for optically modulating the first color light component, the first lens comprising at least one lens element;
a second lens disposed between the two-color light combining means and the three-color light combining means, the second lens comprising at least one lens element; and
a third lens disposed on a light exit side of the three-color light combining means;
the first and third lenses constituting a projection lens;
the second and third lenses constituting a projection lens.
Preferably, this apparatus further comprises color light decomposing/combining means for decomposing white light emitted from a light source into the first color light and the remaining second and third color light components, and emitting thus obtained color light components into two directions different from each other, the color light decomposing/combining means also acting as the three-color light combining means;
the first or second lens being disposed on an optical path of the color light components decomposed and combined by the color light decomposing/combining means.
Preferably, the color light decomposing/combining means comprises a polarization separating/combining device.
Preferably, a polarization converter for converting polarization of light in a specific wavelength band into a polarization direction having a predetermined angle is disposed on a side of the color light decomposing/combining device where a luminous flux from the light source is incident.
The two-color light component combining means may comprise color separating means for decomposing incident light according to a wavelength band thereof.
Preferably, a polarizing plate is disposed on a side of the color light decomposing/combining device where a luminous flux from the light source is incident.
The reflection type light valves may comprise reflection type liquid crystal display devices.